The poor compatibility between plant fibers and polylactic acid (PLA) severely restricts the wide application of PLA composites. The traditional treatment methods generate a large amount of wastewater and cause additional energy waste. This work innovatively proposed the use of reactive epoxy resin groups or isocyanate groups to cross-link with corn stalk fibers (CSF). This treatment formed a core-shell structure, which reduced and coated the hydroxyl groups on the surface of the CSF. Subsequently, high-performance CSF/PLA composites were prepared by in-situ bonding with PLA. The microscopic analysis showed that CF forms a distinct core-shell structure. The results indicate that when 10 % isocyanate was added, and the core-shell structure was formed. The mechanical properties of each phase of the PLA composite could be significantly improved. The impact resistance of the PLA composite was increased by 99.8 % compared to the modified one. The tensile strength and flexural strength reach 50.7 MPa and 113.4 MPa, respectively. Making composites using nature biomass as raw materials is a good way to save energy and solid carbon, while also endowing the materials with rich functionalities, which is beneficial to realize the sustainable development of macromolecular materials.